ALSA: pcm: Return 0 when size < start_threshold in capture

In __snd_pcm_lib_xfer(), when capture, if state is PREPARED
and size is less than start_threshold nothing can be done.
As there is no error, 0 is returned.
Signed-off-by: Ricardo Biehl Pasquali <pasqualirb@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/core/pcm_lib.c

@@ -2173,11 +2173,16 @@ snd_pcm_sframes_t __snd_pcm_lib_xfer(struct snd_pcm_substream *substream,
 		goto _end_unlock;
 
 	if (!is_playback &&
-	    runtime->status->state == SNDRV_PCM_STATE_PREPARED &&
-	    size >= runtime->start_threshold) {
-		err = snd_pcm_start(substream);
-		if (err < 0)
+	    runtime->status->state == SNDRV_PCM_STATE_PREPARED) {
+		if (size >= runtime->start_threshold) {
+			err = snd_pcm_start(substream);
+			if (err < 0)
+				goto _end_unlock;
+		} else {
+			/* nothing to do */
+			err = 0;
 			goto _end_unlock;
+		}
 	}
 
 	runtime->twake = runtime->control->avail_min ? : 1;